Traveling wave tube



Dec. 6, 1955 c. F. QUATE TRAVELING WAVE TUBE F'iled Dec. 7

lNVENTOR C. F. QUA TE By J. Mk5

A TTORA/EV United States Patent ice 26291 Patented Dec. 6, 1955 neticenergy is being extracted from them. A very advantageous arrangement isprovided in conjunction with 2 726 291 these successive circuits forsupplying to them radio frequency signals in the proper phases. Thearrangement TRAVELING WAVE TUBE 5 is an improvement over that disclosedin a copending Calvin F. Quate, Berkeley Heights, N. 3., assignor to 355221 5 3222 3 2:: Z gg gg Kompfner on Bell Telephone Laboratories,Incorporated, New York, p N'Yq a cfimemfion New York A more completeunderstanding of the lnventlon, to-

gether wlth a better appreciation of 1ts advantages Wlll APPliwfimlDeflembel 1953, Serial PIG-396,459 10 best .be gained from a study ofthe following detailed description given in connection with theaccompanying 8 Claims (CL 179-171) drawing in which the single figureshows in schematic form a traveling wave tube employing successiveelectron stream signal wave interaction circuits. This invention relatesto devices utilizing electron Referring now particularly to the drawing,the figure beams and more particularly to traveling wave tubes. shows anillustrative embodiment of a traveling wave An object of this inventionis to improve the efiiciency tube 10 made in accordance with theinvention. In this of traveling wave tubes. embodiment electrons arebeamed by any convenient Traveling wave tube amplification of waveenergy means along an axis enclosed within an evacuated envemakes use ofthe interaction which results between an lope of suitable dimensions.The electrons can be conelectron stream and the electric field of atraveling or fined to the axis of flow by any convenient means suchpropagating electromagnetic wave when the electron as a longitudinalmagnetic field aligned parallel to the stream is beamed in couplingrelation to the wave electric axis. For purposes of simplicity, however,no such means field. When the electron stream is properly synchronizedhas been shown in the drawing. As the electrons travel with thetraveling wave, some of the kinetic energy of along the axis of flowthey are acted upon by successive the electrons is transformed intoelectromagnetic energy. electromagnetic fields maintained around theelectron The electrons, as a result of this transformation, are streamby appropriate means. Here these means include slowed down in proportionto the energy extracted from helices 11, 12, 13, 14, 15, and 16 placedaround electron them. As the average velocity of the electronsdecreases, stream 17 at points successively along its path fromelechowever, they fall more and more out of synchronism tron gun 18 tocollector anode 19. Each of these helices with the traveling Wave untilfinally no useful exchange is maintained at potentials successivelyhigher than the of energy is possible. To compensate for thenonunipotential of cathode or gun 18. That is, helix 11 is formity inthe average velocity of the electrons, it has maintained at a potentialhigher than that of electron gun been suggested that in a conventionalhelical traveling 18, but lower than the potential of helix 12, and eachsucwave tube the pitch of the propagating helix be made to ceeding helixalong the length of the tube from gun 18 vary from greater to smallerdown the length of the electo collector 19 is maintained at a higherelectrical potentron stream. In this manner the axial velocity of thetial than its preceding helix closer to the gun 18. In traveling wavecan be slowed down in proportion to the this embodiment these potentialsare supplied by sources slowing down of the electrons. This arrangementun- 20, 21, 22, 23, and 24 connected to helices 11 through fortunatelysuffers from the disadvantages that the pitch 16 as shown. While thevoltages provided by these taper for efiicient operation is a functionof, among other sources may be equal to each other it should beunderpararneters, steady state beam current. Accordingly, for stood thatthey may be adjusted separately to any desired a given physical helixstructure of this type, there is value when it is convenient to do so.Surrounding. each only one value of beam current and one value of radioof helices 11 through 16 is a respective one of helices frequency powerlevel within a very narrow range, which 25 through 36. By means of theseouter helices radio can be used efficiently. Other beam currents andother frequency signals can be impressed in turn upon the inner powerlevels require difierent helix tapers. As a result, helices and theelectron stream. A radio frequency input the versatility or flexibilityof operation of this kind of signal circuit consisting of hollow waveguide 31 is contubev is undesirably limited. The present invention seeksnected at appropriate points along it to each of helices to provide atraveling wave tube which approaches, al- 25 through 30 by means ofprobes 32 through .37. The though it does not achieve, 100 per centefiiciency, and spacings along the guide between successive probes arewhich is not limited to operation with a single-valued made so that thephases of the voltages applied to helices beam current and single radiofrequency power level. As 25 through 30 have the proper relationship toeach other will appear, one of the advantages of the invention is and tothe phase of the signal propagating along the electhat the tendency ofthe electrons to fall out of synchrotron stream. The amount of thevoltage applied to a nism with the traveling wave field can easily becompenhelix can conveniently be varied by adjusting the depth sated forelectrically rather than in the mechanical way of penetration into theguide 31 of the probe connected suggested previously and outlined above.to the helix. In this manner the efiiciency of operation In accordancewith the present invention, in one speof tube 10 can be maximized byavoiding overbunching cific embodiment thereof, a number of slow wavecircuits of the electron stream. The output ends of helices 25 such aswire wound helices are positioned in succession through 30 are connectedin a way similar to the input along and surrounding the path of anelectron stream. connections by means of probes 38 through 43 insertedin As the electrons pass through each successive circuit they hollowwave guide 44. give up energy to the radio frequency field in thisregion The lengths of helices 25 through 30 and their respecand as aresult their average velocity is decreased. Each tive inner helices 11through 16 should each be substancircuit is maintained at a higherdirect potential than tially one-half the beat wavelength, that is, thewavethat of the preceding circuit so that the electrons when length ofthe standing Wave which would appear on a passing from the electrostaticfield of one circuit to that uniform transmission line made up ofconcentric helices of the next are accelerated by an amountcorresponding such as 11 and 25. The pitches of the two helices comtothe potential difierence between; the two circuits. Thus prising theinner and outer helices of each pair should the average velocity of theelectrons can bev maintained within certain limits even though a largeamount of kibe approximately the same in magnitude but in oppositesense. Under these conditions, wave energy applied to the left orupstream end of an outer helix such as helix 25 will be almost entirelytransferred onto the inner helix such as helix 11 before it reaches theend of the outer helix. Thus, both the input and output ends of theouter helices will be located at voltage antinodes and the ends of theinner helices will be located at voltage nodes. Throughout thespecification the term upstream is used to denote a point or locationcloser to the electron gun than the point or location with which it isbeing compared. Conversely, the term downstream denotes a point orlocation closer to the collector than the point with which it is beingcompared. The beat wavelength is most easily determined by measurementalthough it can be determined in the way disclosed in copendingapplication of R. Kompfner, Serial No. 355,028, filed May 14, 1953.

For eflicient operation of tube 10, the depth of probe 45 into guide 31should be varied until the proper bunching voltage is applied toelectron stream 17 via bunching cavity 46. Sources 20 through 24 mayalso be adjusted individually to insure that the electrons are in propersynchronism with the electric fields traveling down the various helices.The pitch of these helices, of course, determines the velocity at whichthese fields travel which should be approximately equal to the velocityof the electron stream.

As the electrons travel along the path of stream 17, which is congruentwith the common axis of the successive helices, they first come to theregion surrounded by any suitable electron stream bunching means such asthe cavity 46 which is shown or a short helix similar to helix 11 inwhich some of the electrons are retarded and others are accelerated inaccordance with the variations in intensity of the signal wavepropagating along the helix. By this action the electrons are bunchedinto groups which proceed down the tube, being timed by means ofadjustable delay 47 and the gap between buncher 46 and helix 11, toreach the region surrounded by helix 11 at the proper instant to beretarded by the signal wave propagating along the helix. The tubecircuit parameters are arranged so that while within this region theelectrons are decelerated by an amount corresponding to the voltagesupplied by battery 20. The number of times the electrons areaccelerated and decelerated in this way as they travel to the anode 19determines the total amount of energy which can be extracted from themand consequently the amount of wave amplification obtainable.

The degree of bunching of the electron stream produced by buncher 46 isa factor determining the efiiciency of tube 10. As the bunching becomesmore perfect the elficiency increases and this effect makes tube usefulas a high level expander, that is, an amplifier whose gain increases asthe signal level increases.

Helices 11 through 16 provide a desirable way of impressing radiofrequency signal voltages on electron stream 17 because they can beconnected, without additional radio frequency insulating elements,directly to batteries 20 through 24. If desired, however, these helicescan be replaced by appropriate accelerating grids.

The foregoing explanation is intended in illustration and not inlimitation of the principles of the invention. Various changes ormodifications in the embodiment illustrated may occur to those skilledin the art and these changes may be made without departing from thespirit or scope of the invention as set forth. In particular, instead ofhelical wave propagating circuits such as those shown, various otherwave propagating circuits may be used. Moreover, the number of circuitsto be used is not limited to the six shown but may be greater or smallerdepending upon the tube efiiciency required. In general, the larger thisnumber, the greater the efliciency.

What is claimed is:

1. In an electronic device, means for forming and projecting an electronstream, means for bunching said .4 stream in accordance with a signal, aplurality of means located along said stream in field coupling relationthereto for causing interaction between said stream and a singleelectromagnetic wave signal, means for maintaining the averagevelocities of the electron stream at successive points along itapproximately equal to each other, extended input wave guiding means towhich said bunching means and said plurality of means located along saidstream are connected respectively at successive points of proper phaserelation along the wave guiding means, and an extended output waveguiding means to which said plurality of means located along said streamare connected respectively at successive points of proper phase relationtherealong.

2. The combination of elements of claim 1 in which said input and outputwave guiding means are conductively bounded wave guides.

3. The combination of elements of claim 1 in which each of saidplurality of means located along said stream is a pair of concentriccoupled helices surrounding the electron stream.

4. The combination of elements of claim 1 in which said means formaintaining the average velocities of the electron stream are aplurality of direct current voltage sources.

5. The combination of elements of claim 1 in which said plurality ofmeans located along said stream include 4 parallel connected helices ofequal pitches.

6. In a device which utilizes the interaction between an electron beamand an electromagnetic wave to amplify the wave, means for forming anelectron beam and for projecting said beam along a predetermined path,means for bunching the electrons of said beam in accordance with asignal, a plurality of separate interaction circuits arranged in spacedsuccession along the beam paths for propagating electromagnetic waveenergy in coupling proximity with said electron beam, said successionextending along the beam path a distance of several wavelengths andcharacterized in that each of the interaction circuits has substantiallythe same phase velocity propagating characteristics, means formaintaining the average velocity of the electron beam substantially thesame at the upstream end of each of the successive interaction circuitsalong the beam path, an extended input wave guiding means to which saidbunching means and said plurality of interaction circuits are connectedrespectively at successive points of proper phase relation along theWave guiding means, and an extended output wave guiding means to whichsaid plurality of interaction circuits located along said beam path areconnected respectively at successive points of proper phase relationtherealong.

7. In a device which utilizes the interaction between an electron beamand an electromagnetic wave to amplify the wave, means for forming anelectron beam and for projecting said beam along a predetermined path,means for bunching the electrons of said beam in accordance with asignal, a plurality of separate interaction circuits arranged in spacedsuccession along the beam paths for propagating electromagnetic waveenergy in coupling proximity with said electron beam, said successionextending along the beam path a distance of several wavelengths andcharacterized in that each of its interaction circuits has substantiallythe same phase velocity propagating characteristics, means formaintaining each interaction circuit of the succesion at a higher D.-C.potential than the adjacent interaction circuit which is upstreamthereof, an extended input wave guiding means to which said bunchingmeans and said plurality of interaction circuits are connectedrespectively at successive points of proper phase relation along thewave guiding means, and an extended output wave guiding means to whichsaid plurality of interaction circuits located along said beam path areconnected respectively at successive points of proper phase relationtherealong.

8. In a device which utilizes the interaction between an I electron beamand an electromagnetic wave to amplify the wave, means for forming anelectron beam and for projecting said beam along a predetermined path,means located along said path for bunching said electron beam inaccordance with a signal, a plurality of pairs of helices spaceddownstream from said bunching means and arranged in spaced successionover a distance of several operating wavelengths along the beam path forpropagating electromagnetic wave energy in coupling relation with saidbeam, the two helices of each pair having unequal radii and beingpositioned coaxially and substantially coextensively along a portion ofthe electron beam for forming a concentric pair having inner and outerhelices, the pitch of the inner and outer helices of each of theconcentric pairs being equal and of op posite sense, means formaintaining one helix of each References Cited in the file of thispatent UNITED STATES PATENTS 2,489,082 De Forest Nov. 22, 1949 2,584,308Tiley Feb. 4, 1952 2,588,832 Hansell Mar. 11, 1952

